A mixture of phosphate buffer, copper sulfate and pyridine was shown to catalyze an unusual cis-ring opening of several aryl oxiranes. The reaction was also used to introduce chloride, methoxide and hydroxide at the benzylic center of indene oxide, while adding a proton at the oxirane oxygen. A chiral modification of this reagent (copper sulfate-nicotine) was used for the asymmetric synthesis of (plus)-1,2-indene oxide and (plus)-cis-1,2-indanediol. A series of substituted threo-R, R-diphenylethane diols, prepared by microbial reduction of the appropriate benzil derivatives, was converted to the corresponding substituted trans-(R,R)-stilbene oxides. The positive CD bands at 230-235 nm exhibited by these compounds agrees in sign and magnitude with those predicted from a model developed by Mason et al. for trans-stilbene oxide. Microbial reduction of p-methyl desyl chloride was shown to yield the threo-(R,R)-chlorohydrin, thus establishing a route for the preparation of optically active substituted cis-stilbene oxides. The sterochemistry at the ring-junction of an aldol product from the reaction of 1-morpholino-1-cycloheptene and methyl vinyl ketone was determined by X-ray crystallography as trans.